Data communication via satellite has grown with leaps and bounds recently. That growth has reduced transmission costs and increased usage, but at the cost of bandwidth congestion. In part, the congestion is due to an operation environment that utilizes static channel assignments with scheduling based on manual time reservation mechanisms.
For example, in the past, distributing television, cable, and other video/sound files to local stations around the country has been done by manually scheduling the feeds. Typically, a satellite transmitter has a fixed allocation of bandwidth and, if a user needs to transmit ten minutes worth of data, the user manually places a phone call to a provider and indicates that he or she would like ten minutes of transponder time at a specified time (e.g., 4:00 p.m.). This negotiation for transponder time is time consuming and inefficient and may result in the user being forced to purchase an hour's worth of transponder time when all that is needed is ten minutes. Consequently, once the user finishes transmitting his data, the transponder sits dormant for the remaining fifty minutes, which results in wasted capacity. Currently, no providers have a system that promotes the efficient use of transponder time through the reuse and sharing of previously dedicated facilities.
Some alternative satellite providers are looking at reliable multicast transmission as a key technology that may be used to minimize network traffic. Coordination is a major problem with multicast file distribution over a satellite. In other words, the problem is how can many content providers (e.g., channels, news organizations, etc.) distribute their content without overwhelming the network bandwidth. This is especially a problem where bandwidth allocation is handled through a manual system.
A second problem in multicasting files over a satellite communications network is that you cannot determine exactly when your file is sent. No one can know with certainty when a particular transmission will end. In the past, people have dealt with this problem by statistically evaluating the data transmission information to determine a statistical end point over time. That is, by looking at a number of transmissions after the fact, one can figure out how many actually went through on time. Usually, that percentage is very high, approximately 90%. It can be made even higher, but the trade-off typically is a less efficient use of satellite transponder time. In other words, if you want to be certain that your file will be sent over the satellite when you schedule it, you need, overall, to schedule less traffic than the system can handle. In essence, this is very like what a doctor does in scheduling patient appointments—if the doctor wants to make sure he or she sees the maximum number of patients, the doctor will schedule many appointments for the day. But, as the day progresses, the delay between when the doctor sees the patients and the patients' appointment times lengthens. The doctor can remedy this by reducing the number of appointments, but then the doctor runs the risk of having some down time during which no patient is scheduled.
In any event, if bandwidth is allocated based on these statistical averages, inevitably some jobs will not be completed within the allocated transmission time. Skilled persons in this art say this means that your file completion times are “non-deterministic.” Non-deterministic file transmission causes scheduling difficulties in projecting future start times for other data transmission. This can be a critical problem. For instance, consider a breaking news story, such as a presidential news conference, that a network wants to be certain is sent out across the country to various local affiliates. It is critical that the network knows that at the set time the news story will be transmitted. You would normally think that to guarantee files are sent on time, and thus solve the scheduling problems described above, one could just increase the rate the data is sent over the satellite. But this brings up another problem with multicast, which is that data throughput varies. For example, suppose five out of six cable headends where the cable equipment operators maintain their equipment have state of the art, well maintained equipment that can receive data at 100 Mbps (one Mbps is equivalent to one million bits of data per second). One of the six head ends can only receive data at 10 Mbps. In this situation, if all six need to receive the file within a certain designated time, increasing transmission bandwidth does not guarantee a transmission stop time because there is a “weak link in the chain,” namely the 10 Mbps head end.
Conventional systems do not provide efficient or optimum resource allocation when multiple local demands are placed on a control system. International Application Serial No. PCT/US00/10394, published as International Publication No. WO 00/67449, filed Apr. 18, 2000, which is hereby incorporated by reference in its entirety, addressed some of the above-identified problems by introducing dynamic rate allocation, dynamic time slicing and logical framing, and distributed hierarchical control. However, there remains room for improvement. More specifically, optimizing available multiple satellite resources across a diverse satellite distribution network is not provided for by International Application Serial No. PCT/US00/10394. Additionally, applications such as providing access to multiple satellite resources using multiple uplink sites and creating a content distribution network utilizing content from multiple content providers are not disclosed in International Application Serial No. PCT/US00/10394.
Many broadcast communication satellites used for transmitting multimedia information operate in an orbital plane known as a geo-synchronous or geo-stationary orbit. Such satellites operate within the equatorial plane of the earth and their transmission is designed for maximum signal strength within a beam or footprint that covers a predetermined portion of the earth's surface. An example is a satellite beam designed to cover the continental United States, such a beam being generally referred to as a CONUS beam. However, because satellite communication requires line-of-sight transmission between the receiver antenna/dish on the earth's surface and the orbital position of the satellite, a receiver can only receive one transmission from one satellite at a time. This limitation may be overcome by using multiple antennas and receivers with each antenna aligned with a different satellite.
With multicast file distribution, there exists centralized control for the multicast distribution session, even when there is more than one physical outbound distribution channel (e.g., multiple satellite uplink sites). In multicast file distribution over a satellite network where the desired receivers are dispersed over multiple satellite beams, there exists a multicast scheduling problem. The scheduling problem arises from a lack of coordinated control between the centralized multicast distribution site and the multiple satellites that can collectively transmit to the desired pool of receivers. There are many instances where a user may wish to send a multicast transmission to geographically diverse receive sites that cannot be covered by any one satellite transponder. In such cases, it is desirable to maintain efficient use of required satellite resources.
To address the identified problems, the present invention provides a distributed-hierarchical scheduling control system that monitors the network and adapts dynamic rate allocation, frequency allocation, satellite allocation, time slicing, and logical framing to optimize system resources.